The present invention relates generally to hydraulically-actuated fuel injection systems and, more particularly, to devices and methods for eliminating the phenomenon known as xe2x80x9ccacklexe2x80x9d.
Hydraulically actuated electronically controlled unit injectors (HEUI injectors) are known in the art. See U.S. Pat. No. 5,492,098 to Hafner et al., incorporated herein by reference. Engines with HEUI injectors are known to produce a noise referred as cackle when the fuel injected during the pilot or pilot portion of an injection event is insufficient to initiate combustion. The main injection portion of the injection event that follows such pilot injection typically produces a higher rate of pressure rise than is experienced following normal pilot injection. The higher rate of pressure rise during main injection results in an audible cackle sound that can be misinterpreted as a major engine mechanical problem. The cackle phenomenon is not harmful to the engine, but the sound has caused user concern and has resulted in unnecessary visits to dealers with perceived engine problems which in turn has resulted in increased (and unnecessary) warranty costs for engines in the field with HEUI injectors.
Cackle is a phenomenon which occurs if the pilot injection for a particular cylinder is compromised due to incomplete fill of the fuel pumping volume (the high pressure pump chamber) in the HEUI injector. This manifests itself in insufficient fuel injected into the cylinder to initiate combustion with the pilot injection alone and consequently the ensuing main injection yields a higher rate of cylinder pressure rise than other cylinders, thereby causing a non-rhythmic noise that is frequently misdiagnosed as a major mechanical problem. The partial noise that is frequently misdiagnosed as a major mechanical problem. The partial fill of the injector pumping volume that results in cackle may be caused by one of the following:
low fuel pressure resulting from fuel pump, pressure regulating valve or check valve problems;
high fuel pressure fluctuation (adverse fuel rail dynamics) caused by disturbances of nearby cylinders (cylinder 6 to cylinder 8, for example); or
other deficiencies, for example, combustion gas leakage past a copper injector gasket.
Note that the firing order in a typical V8 type engine is 1-2-7-3- 4-5-6-8. The number six cylinder and the number eight cylinder are immediately adjacent to one another on the left bank of cylinders. Accordingly, it is the high pressure fuel spill of the number six cylinder immediately preceding the filling of the pumping volume of the number eight cylinder that can cause high fuel pressure fluctuation, resulting in the partial fill of the pumping volume of the number eight cylinder. This results in cackle experienced in the number eight cylinder. Note further that such engines have incorporated substantially identical injectors to serve each of the cylinders.
In the past, certain engines have utilized a fuel pressure accumulator to eliminate the cackle problem. Engines, including the engine described hereinafter, have incorporated check valves, a dead-headed fuel system, and fuel system calibration to help reduce cackle. However, these expedients still have not fully resolved the cackle problem and there is still a need for a solution to the cackle problem.
The present invention substantially meets the aforementioned needs of the industry. Controlling the quantity of fuel injected during the pilot portion of the injection event has been determined to be the critical factor in eliminating the cackle sound. Installing an injector with a long lead in the cackling cylinder assures an adequate quantity of fuel injected during the pilot portion of the injection event to ensure ignition of the pilot portion and thereby eliminating the cackle sound that occurs during the ensuing portion of the injection event. The injector of the present invention increases injector lead and thereby increases the quantity of fuel injected during the pilot portion of the injection event. This cures cackle because it assures that sufficient fuel is injected initially during the injection event to support combustion during the pilot portion of the injection event, without regard to adverse fuel rail dynamics.
The present invention is a fuel system for a diesel engine having a plurality of combustion chambers, the engine having ignition cackle occurring in at least one combustion chamber includes a standard fuel injector being associated with each of the non-cackling combustion chambers, and a non-standard fuel injector being associated with each of the cackling combustion chambers, each of the non-standard fuel injectors having an increased pilot volume of fuel, the increased pilot volume of fuel having a quantity of fuel therein for injection into the associated combustion chamber. The present invention is also a non-standard fuel injector and a method for affecting cackle.